Applicant's prior U.S. Pat. No. 4,386,901 makes reference to useful background art and a loose bearing mounted vibrating shaft supported within an elongated open frame. Such patent was directed to a highly maneuverable screed particularly for use with so-called wet or "mud" type screeding in which forms are not available or used. With a continuing and substantial increase in residential, institutional and business construction there remains a need for a portable vibrating concrete screed of extremely light weight, of simple construction, of low cost and for use on relatively small jobs for screeding wet concrete confined by forms.
The present invention is to a great extent based upon use of a unique extruded member. This unique extrusion by itself and without added structure provides an enclosed vibrating shaft bearing mount and housing, screed surfaces, surfaces for slidably supporting the screed on forms, an engine mounting and a handle mounting surface.
Reference is next made to prior art screeds having some form of extrusion as a structural element. In this regard, U.S. Pat. No. 2,542,979 illustrates a structural T-beam mounting and welded to a separate cylindrical pipe. The T-beam provides screed surfaces. Auxiliary structure appended to the fabricated pipe/T-beam is required for mounting an electrically driven vibrator and for supporting the screed on forms. U.S. Pat. No. 2,693,136 illustrates a similar fabricated pipe/T-beam with an auxiliary structure for mounting a gasoline engine driven vibrator. U.S. Pat. No. 3,095,789 in a further example incorporates a fabricated hollow beam with auxiliary structure on which magnetic vibrators are mounted. In a further example found in U.S. Pat. No. 4,105,355 a fabricated hollow beam mounts within the beam a vibrating shaft with eccentric weights. The base of the fabricated beam is formed with attached angle pieces for supporting the screed on forms and a central bottom cover for use as a screeding surface.
Considering all of the mentioned prior art which is believed to be typically and sufficiently representative of the prior art, it can be seen that the typical portable screed is made up by fabricating and assembling a multitude of separate parts whereas the present invention recognizes that it would be desirable from the viewpoint of reducing weight, minimizing cost and improving overall portability to reduce the number of components required. All of the cited extruded elements of the prior art have the disadvantage of requiring add-on mechanically secured or welded on parts such as angle pieces, pipes, bottom plates and the like to provide a screed surface, an engine mounting surface, handle mounting surface and means for mounting a shaft type vibration source. On the other hand as the present invention recognizes, it would be desirable to provide a screed having an extruded element formed in such a way as to be slidable on forms and to provide without requiring add-on parts a screed surface, an engine mounting surface, a handle mounting surface and a housing for supporting internally of the extruded element a vibrating shaft and its bearings.
The object of the present invention thus becomes that of providing a further improved, lightweight, highly portable screed designed for use in wet screeding with forms. A more specific object becomes that of providing a portable concrete screed utilizing a uniquely formed extruded element which serves the several functions of being a screed, providing a housing for a vibrating shaft and its bearings, providing a mounting for handles for guiding and manually propelling the screed during use and providing an engine mount. Other objects will become apparent as the description proceeds.